1. Field of the Invention
The present invention relates to objects which should be prevented from being forged and are to be checked for authenticity, such as important documents, securities, paper money, checks, traveler's checks, bank cards, prepaid cards, ID cards, CD cards, credit cards, passports, art objects, and betting tickets for public-managed gambling games (e.g., horse racing and bicycle racing). The present invention also relates to a method and apparatus for checking the objects.
2. Description of the Related Art
A checking method and apparatus utilizing microwaves are known in the art as measures for checking the authenticity of documents or the like, as described in PCT National Publication No. 63-501250 (i.e., U.S. Pat. No. 4,820,912). An object to be checked, wherein stainless steel fibers are embedded and scattered in the sign panel of a card base member, is also known in the art, as described in Jpn. Pat. Appln. KOKAI Publication No. 5-270181.
According to these publications, microwaves are applied to a large number of metallic wires which are embedded and scattered at random in a document or a card, and a proper digital mark responsive to a response microwave bundle is recorded in a suitable region of the document or card according to specific rules. To check the authenticity of the document or card, microwaves are applied to the document or card, and a response microwave bundle is collated with the digital mark. The document or card is determined as being authentic when the microwave bundle and the mark agree with each other.
The checking means which utilizes microwaves, as in the apparatuses of the above publications has problems in that the measurement of a response microwave bundle is susceptible to external noise, and the signal-to-noise ratio (S/N ratio) is lowered thereby. In addition, the apparatuses of the publications may constitute a source of noise since they oscillate microwaves. Further, a microwave transmitter and a microwave receiver are generally large in size and entail high costs.
In the case where metallic wires are embedded in a thin object, such as paper, it is likely that the metallic wires will be exposed in the surface of the object. If this happens, the object does not look nice. In addition, the metallic wires prevent satisfactory printing or coloring from being performed with respect to the object, and may rust, depending upon the environment. Further, if the object is bent, the metallic wires embedded therein may break, protruding from the surface of the object. In the worst case, the code which is assigned to the object in the manufacturing process of the object changes into a different code, and the collation of the code of the card cannot be performed.
On the sign panel of a cash or credit card, a certain kind of data (e.g., a user's name) is written with a writing tool, such as a ball-point pen or a fountain pen. Therefore, the sign panel should be white or whitish. However, if metallic wires, such as stainless steel wires, are embedded in the white or whitish sign panel, they may be externally observed. It should be also noted that the sign panel is thin and the metallic wires embedded in the sign panel may be exposed in the surface of the sign panel. Accordingly, the use of metallic wires is not desirable from the viewpoint of security.
Since metallic wires have a smooth surface, they may hinder a user's name or the like from being clearly written on the sign panel, or may become a cause of ink blotting. In addition, if a sign panel block containing metallic wires is cut into sign panels of desirable size by means of a cutter, the metallic wires may partially project from the faces along which the sign panel block is cut. Further, the cutter does not withstand long use.
If the metallic wires are thin, the problems mentioned above may be solved to a certain degree, but the use of thin metallic wires in no way provides a perfect solution to the problems. In addition, the use of thin metallic wires is not realistic since it results in both a poor S/N ratio and a high manufacturing cost.